DIM for Estrogen Balance: The 130-Woman Tamoxifen Trial Result

Written by CV Blogger · Published 17 October 2026 · Last updated 17 October 2026

In a 130-woman randomised trial published in 2017, DIM raised the urinary 2/16α-hydroxyestrone ratio, the estrogen-metabolite marker it is sold to shift, and in the same women it lowered blood levels of endoxifen, an active form of the breast-cancer drug tamoxifen. Diindolylmethane (DIM) is a compound the body forms from indole-3-carbinol, a substance in broccoli, cabbage and other cruciferous vegetables, and it is sold in capsules marketed for “hormonal balance”, including the 400 mg-per-serving product reviewed here.

What DIM Is, and What the Vegetable Version Does and Doesn’t Tell You

According to Memorial Sloan Kettering Cancer Center (MSK, updated 15 December 2023), DIM is a metabolite of indole-3-carbinol (I3C) and “the most studied of all I3C metabolites.” I3C comes from glucosinolates in cruciferous vegetables. The Linus Pauling Institute (LPI, reviewed July 2017) explains that in stomach acid I3C molecules combine with each other, and one product is DIM.

The National Cancer Institute’s cruciferous-vegetable fact sheet (NCI, reviewed 7 June 2012) says studies of vegetable intake in humans “have shown mixed results.” The LPI adds that the amount of I3C formed from food “is variable.” A finding about broccoli cannot simply be transferred to a 400 mg capsule.

Mayo Clinic, “Mayo Clinic Minute: Cruciferous finds at the farmers market.” About the vegetables, not DIM capsules; we could not read a transcript, so treat it as context, not evidence.

Does DIM Change Estrogen Metabolism? Yes, the Marker Moves

This is the part of the DIM story that holds up. The body breaks estrogen down along several paths, and two of the products measured in urine are 2-hydroxyestrone (2-OHE1) and 16α-hydroxyestrone (16α-OHE1). The LPI describes 16α-OHE1 as “highly estrogenic” and 2-OHE1 as less so, and says it has been hypothesised that shifting metabolism toward the 2 path could lower the risk of estrogen-sensitive cancers. That is a hypothesis. What the trials do show, per the LPI, is that oral I3C or DIM “has consistently increased” urinary 2-OHE1 or the 2:16 ratio in women.

Two cautions apply. The first three rows are small or specific populations, and the last is observational, with people reporting their own DIM use. Every result is also a urinary biomarker: none of these studies measured whether anyone felt better or avoided a disease. The Newman and Smeaton authors state that “research into DIM’s effect on the estrogen profile is lacking in the published literature.”

Does a Moved Marker Mean a Health Benefit? What the Outcome Trials Found

The LPI (reviewed July 2017) answers the marker question directly: “large case-control and prospective cohort studies have failed to find significant associations” between the urinary 2:16 ratio and risk of breast and endometrial cancer. A ratio that moves is not the same as an outcome that improves.

Where DIM has been tested against actual outcomes, the results are unimpressive. In a randomised trial of 64 women scheduled for a procedure on biopsy-proven cervical lesions, DIM at about 2 mg/kg a day for 12 weeks was well tolerated, and the authors reported that “There was no statistically significant difference in any outcome between the DIM and placebo group” (Del Priore et al., Gynecologic Oncology, 2010). Many women in both arms improved. The LPI also describes a six-month randomised trial of 150 mg/day in 551 women in which DIM “failed to promote HPV clearance.” MSK says studies are “mixed” for cervical cell abnormalities and that “clinical data are limited.”

Taken together: DIM reliably shifts a laboratory marker, and no trial cited here shows that the shift translates into a benefit a reader would notice. Nor did any source we read include a controlled trial in men, so the “both men and women” framing used for this kind of product rests on thinner ground than the women’s data above.

Tamoxifen, Hormone Therapy, Pregnancy and Other Cautions

The same property that makes DIM interesting, its effect on how the body handles estrogen and drugs, is the source of its main cautions.

• Estrogen therapy. In a 2025 observational study of 1,458 postmenopausal women using a transdermal estradiol patch, the 108 who also took DIM had significantly different urinary estrogen profiles; the authors warned of “unexpected changes” and a possibility that the effect might “decrease the overall estrogenic impact” of hormone therapy (Newman and Smeaton, Menopause, July 2025). It is one retrospective study, not proof.
• Other medicines. MSK says DIM modulates several CYP450 liver enzymes and may make drugs processed by them less effective, and it advises women on birth-control pills to check with a clinician first.
• Pregnancy and breastfeeding. MSK: “Because of potential hormonal effects, women who are pregnant, planning to get pregnant, or nursing should not take DIM.”
• Case reports. MSK lists a visual disturbance (central serous chorioretinopathy) after two months of excessive daily intake that resolved 8 weeks after stopping, a drug rash with eosinophilia, an ischaemic stroke in a 38-year-old woman, and a pulmonary embolism with deep-vein thrombosis in a 65-year-old man. Case reports cannot show that DIM caused these events.
• Long-term unknowns. The LPI notes that contradictory animal results led several experts to caution “against the widespread use of I3C and DIM supplements in humans until their potential risks and benefits are better understood.”

Tolerability in the trials was generally good: Del Priore reported nausea in 2 of 64 women, and Thomson reported minimal adverse events that did not differ from placebo.

Inside NatureBell DIM 400 mg: Label Versus Listing

The product is NatureBell DIM 400 mg with broccoli and black pepper extract, 240 vegetarian capsules. Its Supplement Facts panel gives a serving as 2 capsules and 120 servings per container: DIM (as diindolylmethane) 400 mg, broccoli powder 25 mg and black pepper extract (Piper nigrum) 2.5 mg, each with no Daily Value established. Other ingredients are rice flour, magnesium stearate, silicon dioxide and a vegetable cellulose capsule. At 2 capsules a day the bottle lasts 120 days; each capsule holds about 200 mg of DIM.

No RDA, Adequate Intake or Tolerable Upper Intake Level exists for DIM because it is not a nutrient. The 400 mg serving is the highest single daily amount in this comparison, 1.3 times the 300 mg used for 14 days (Rajoria) and 12 months (Thomson), and 3.7 times the 108 mg pilot dose. We found no controlled trial at 400 mg. The trials also used a specific absorbable preparation (BioResponse-DIM), and we have no data showing this product delivers the same blood levels.

The listing’s directions (2 capsules daily with a meal) and 120-day claim match the panel, and the capsule is vegetable cellulose, so “vegetarian” holds. Under DSHEA, the FDA (FDA, content current as of 21 October 2022, accessed 17 October 2026) does not approve dietary supplements before they are marketed. Not verified: this product’s potency, purity, contaminant testing or the source of its DIM.

Who Might Consider It, and Who Should Skip It

NatureBell DIM 400 mg with Broccoli and Black Pepper Extract, 240 Capsules

400 mg DIM, 25 mg broccoli powder and 2.5 mg black pepper extract per 2-capsule serving; 120 servings. Browse more women’s health supplements.

View Product Details

Frequently Asked Questions

What is DIM?

Diindolylmethane (DIM) is a compound formed in the stomach from indole-3-carbinol, found in cruciferous vegetables such as broccoli and cabbage. Memorial Sloan Kettering (December 2023) calls it the most studied I3C metabolite. It is sold in capsules marketed for estrogen metabolism.

What does DIM do to estrogen?

Trials show DIM raises the urinary ratio of 2-hydroxyestrone to 16α-hydroxyestrone. In the 2017 trial of 130 women, the ratio rose significantly versus placebo. These are laboratory markers; the trials cited here did not show a symptom benefit or a change in disease outcomes.

Does DIM balance hormones?

It changes how estrogen is broken down, but “balance” is a marketing term, not a measured trial outcome. The Linus Pauling Institute (July 2017) found large studies had not linked the urinary ratio to cancer risk, so a shifted ratio is not proof of better health.

Is DIM safe to take every day?

Trials of 14 days to 12 months reported mostly mild effects, but the 2017 trial authors noted limited long-term safety data, and MSK lists case reports of rash, vision disturbance, stroke and blood clots.

Can I take DIM with tamoxifen?

It is not advised without your oncologist. In the 2017 randomised trial, plasma endoxifen, 4-hydroxytamoxifen and N-desmethyl-tamoxifen were lower in women taking DIM than placebo (p < 0.001), and the authors said the effect on tamoxifen’s benefit needs study.

Can men take DIM?

The studies in this article enrolled women, so evidence for men is thin; MSK describes only limited human data in prostate cancer. Men with hormone-related concerns should have levels checked by a clinician.

Does DIM help with menopause symptoms?

No trial cited here tested menopausal symptoms. A 2025 study found DIM changed estrogen metabolites in women using an estradiol patch and warned it might reduce the effect of hormone therapy.

Does DIM detox the body?

No evidence supports this. Memorial Sloan Kettering (updated 15 December 2023) states, “There is no scientific evidence to back this claim.” DIM does alter how liver enzymes process some drugs, which can matter for medicines.

This article is for educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure, or prevent any disease. These statements have not been evaluated by the Food and Drug Administration. Talk to your doctor before starting any new supplement, especially if you take tamoxifen, hormone therapy or other prescription medication, are pregnant or breastfeeding, or have a hormone-sensitive condition.